luokai0 Composites Expert
Before Starting
- Which fiber? (carbon, glass, aramid)
- Which matrix? (epoxy, thermoplastic, ceramic)
- Structural design or manufacturing focus?
Core Expertise Areas
Fiber and Matrix Materials
Carbon fiber: high stiffness and strength, low density, expensive, brittle. Glass fiber: lower stiffness than carbon, cheaper, good impact resistance. Aramid fiber: Kevlar, high toughness, good impact, poor compression. Epoxy matrix: most common thermoset, good adhesion, brittle, limited temperature. Thermoplastic matrix: PEEK, recyclable, tougher than thermoset, higher cost.
Micromechanics
Rule of mixtures: E1 = Ef times Vf plus Em times Vm for longitudinal modulus. Transverse modulus: inverse rule of mixtures, matrix dominated. Longitudinal strength: fiber dominated, approximately Vf times sigma_f_ult. Fiber volume fraction: typically 55-65% for aerospace structural laminates.
Classical Laminate Theory
ABD matrix: A membrane stiffness, B coupling, D bending stiffness. Ply angles: 0 for axial, 90 for transverse, plus minus 45 for shear. Symmetric laminate: B = 0, no bending-extension coupling. Balanced laminate: equal plus and minus angle plies, no shear-extension coupling. Failure criteria: Tsai-Wu or Tsai-Hill for ply-level failure prediction.
Manufacturing
Hand layup: manual ply placement, low cost, labor intensive, variable quality. Autoclave cure: high pressure and temperature, aerospace quality, expensive. RTM: resin transfer molding, inject resin into dry fiber preform. Filament winding: continuous fiber wound over mandrel for pressure vessels and pipes. AFP and ATL: automated fiber placement and tape laying for large structures.
Best Practices
- Design laminate with at least 10% fibers in each principal direction
- Avoid grouping more than 4 plies of same orientation to reduce matrix cracking
- Account for moisture absorption effect on matrix-dominated properties
- Specify non-destructive inspection method for critical composite structures
Common Pitfalls
| Pitfall | Fix |
|---|---|
| Applying isotropic analysis to anisotropic laminates | Use laminate theory for accurate stiffness prediction |
| Ignoring compression strength reduction | CFRP compression strength much lower than tension |
| Wrong cure cycle causing residual stress | Follow manufacturer cure cycle exactly |
| No impact damage assessment | BVID dramatically reduces compression strength |
Related Skills
- metals-expert
- ceramics-expert
- aircraft-structures-expert